RECENT ADVANCES IN GEOLOGY. 453 
the extinct Proboscidians and Ruminants. None of these 
large animals could probably have passed over the straits 
which now divide these regions, and the close alliance in 
form would indicate a common origin. We infer, therefore, 
that the subsidence during the Drift Epoch cut off the com- 
munication between the two hemispheres, and the refrigera- 
tion which then took place, served to disperse the colossal 
animals, who sought by migration to lower latitudes a cli- 
mate congenial to their nature. 
s in Europe we find the remains of these northern types 
intermingled with those of an African type— the hippopota- 
mus, which in his summer migrations strayed as far north as 
England; so on this continent we had, during this epoch, 
the great sloths, represented by the megalonyx and mylodon, 
whose congeners at this time exist in South America. Thus 
there was an inosculation, so to speak, of two distinct and 
contemporaneous faune. 
It is an inquiry of the highest interest— perhaps as much 
so as any connected with the physical history of the past: 
How far has man been a witness of these stupendous changes ? 
It is not until towards the close of the Drift Epoch, that we 
are enabled to detect unmistakable signs of his works, 
although there are not wanting proofs which would refer his 
origin to an earlier date— the Pliocene. So numerous and 
well-attested are the facts, that we must now regard him as 
the contemporary of many of the great mammals which 
have ceased to exist, and the subject of physical conditions 
very different from what now prevail. To account for these 
changes requires the lapse of a longer period of time than 
has heretofore been assigned to his existence upon earth. 
Thus within a few years has been opened a sphere of in- 
vestigation which has enlisted a large class of able observers, 
and their labors have thrown a flood of light upon the 
origin of our race. Ethnography has become aggrandized 
into one of the noblest of sciences. However conflicting 
these revelations may be to our preconceived notions, they 
